The present invention relates to a device for applying pressure to toner fixation rollers that fix unstable toner that has been transferred to a copy paper from a picture recording device of an electrophotographic copying machine or laser printer.
A variety of copying machines and laser printers are widely available with picture forming devices based on an electronic photographing system. In general, such an electrophotographic device causes the photoreceptor to be uniformly charged before causing either the draft picture to be exposed to a light source or the recorded information to be converted into optical data. This causes a static latent image to be formed on the photoreceptor by radiating light onto it. Such a latent image formed on the photoreceptor is then visualized by means of a developer unit after the adhesion of color pigment toner onto it. Such a visible image, i.e., toner image, is first transferred onto copy paper and then conveyed to a fixer along with copy paper for fixing the image
Conventionally, both pressure and heated fixing methods are well-known. A heated fixer is provided with a pair of rollers which cause toner to be fixed onto the copying paper by means of heating the roller which is in contact with the toner at a constant temperature. The toner fixation system also applies a considerable amount of pressure to the pair of rollers so that the toner image can be stably fixed onto the copy paper by the pressure. Depending on the configuration of either the copy machine or the laser printer, the device may be divided into upper and lower parts along the copy paper transport path, the upper part being supported by a shaft against the lower part so that the upper part can be opened and closed against the lower part. Such a configuration allows misfed paper to be easily removed merely by opening the device. In addition, such a device also has an advantage in that component parts can be easily replaced during maintenance and servicing.
Conventional devices normally apply pressure to a toner fixation roller and release pressure from it by interconnecting the device with an opening and closing mechanism. For example both ends of the upper frame are bent to push the upper toner fixation roller downwards. Spring force is then applied so that it presses against the lower toner fixation roller with an adequate amount of pressure. Consequently, when the upper frame is opened, pressure on the upper toner fixation roller is released, and when the upper frame is closed, an adequate amount of pressure is again applied to the toner fixation roller. Nevertheless, in a device having the configuration mentioned above, the position of the bent portion of the upper frame cannot always be maintained accurately, thus causing a certain differential pressure to be generated in the direction of the shaft of the toner fixation rollers. Likewise, there is a problem with respect to the strength of the bent portion used for applying pressure. This problem is normally caused in applying pressure to the toner fixation roller by using the upper frame itself.